Well, a declaration is just a declaration - not a definition. If you add prototypes to the declaration, the declaration *is* a definition wrt the prototype part, although the subroutine body (i.e. the content of the coderef in the CODE typeglob slot) still isn't set up for lack of code to be compiled. That would be done later, in the definition. Prototypes set up earlier (via declaration) have to match, then.